Glen,
I’m not exactly sure what is confusing you regarding the methodology and value for the BSSI. But I’ll go ahead and run through this again.
No contradiction whatsoever was made from my previous post. I stated no observations north of the preexisting outflow boundary from downstream convection were considered when determining the BSSI. Yes, obviously observations south of this boundary were considered as I mentioned in the previous post. The observation at Winfield was considered when we determined the BSSI, but not used as face-value to completely represent the true value ingested into the mesocyclone. In addition, we collected data northeast of the mesocyclone and south of the supercell FFD in a narrow region which provided true inflow air within 10 minutes prior to tornadogenesis.
With that being said, two variables 1) anvil shadow 2) left-split supercell south of the preexisting outflow boundary lowered the surface temperature from the observation at Winfield. Previous investigations by Markowski et al. (1997) showed surface temperature decreases of 3°C or more occurred beneath storm anvils compared to the observations outside of the shadow. In this case, if we take the sunny sky Winfield observation of 88°F, and apply this research to this example, the value in the anvil shadow south of the Mulvane tornado is around 82.6°F. The data we collected while in storm inflow prior to tornadogenesis suggested the surface temperature was near 80°F. However, I acknowledged in the paper that some of this air was hypothesized to potentially have mixed with some RFD origin air. Therefore, it was a relatively easy conclusion to define the BSSI ingested at the time of the tornado to be around 82°F.
Glen wrote:
“Are you suggesting that if that had been the thermal character of the inflow that the storm could not have produced a tornado?â€
“Could not have produced†is a tricky statement and one I will avoid using. However, lower LCL heights were present than the observation you mentioned at Winfield. Therefore, I will say it’s a safe assumption that several variables, including the lower surface temperature found with the BSSI, aided in an environment more favorable than the surface environment found at Winfield for tornadogenesis.
Lastly, I should again remind you when Markowski et al. (2002) defined the methodology of the “normal†storm inflow value, he acknowledged the following…
“There is more than one way to estimate the base state (and all techniques are arbitrary and imperfect). It maybe somewhat unconventional to specify a reference state that is not constant in space of time, but the choice is as arbitrary as the decision to make the reference state a constant with respect to space or time. It is believed that what is important is not so much the exact way the base state is specified, but rather that the base state is consistently specified and the differences between the cases are examined.â€
I'm hoping this helped clarify the methodology and value determined for the BSSI. And again, excellent questions! Take care!
Scott Blair
http://www.targetarea.net/